April 2021 First Edition; April 2021 © Copyright notice The contents of this paper are copyrighted by Western Dredging Association, WEDA. All rights reserved. Please obtain written permission from WEDA prior to reproducing this document or any part thereof. Citation WEDA’s Technical Report: “Reservoir Dredging: A Practical Overview”; WEDA, 2021 Available online at: www.westerndredging.org Western Dredging Association – WEDA P.O. Box 1393 Bonsall, CA 92003 United States of America Phone: (949) 422-8231 E-mail:[email protected] Web: www.westerndredging.org Photograph on front cover: “Hydraulic Dredging of the Strontia Springs Reservoir, Colorado, U.S.A.” By: Sevenson Environmental Services, courtesy of Denver Water. TABLE OF CONTENTS 1 Introduction ................................................................................................................................ 1 1.1 The Fundamental Problem of Reservoir Sedimentation ...................................................................... 1 1.2 The Goal of Sustainable Reservoir Management .................................................................................... 2 1.3 Dredging as Reservoir Management Tool ................................................................................................. 3 1.4 WEDA – Western Dredging Association ..................................................................................................... 3 1.5 Working Group on Reservoir Dredging...................................................................................................... 4 Acknowledgements ......................................................................................................................................................... 4 2 Linking Reservoir Sedimentation and Maintenance: Sedimentation Management ............................................................................................................................... 5 2.1 Process of Sediment Accumulation in Reservoirs ................................................................................... 5 2.2 Impacts of Sedimentation on Reservoir Function .................................................................................. 6 2.3 Current Tools and Practices for Reservoir Sediment Management .............................................. 10 2.4 Considerations for Evaluating Reservoir Sediment Management Options ............................... 12 2.5 Sustainability of Solutions to Reservoir Sedimentation .................................................................... 13 2.6 Environmental Impacts of Solutions to Reservoir Sedimentation and Associated Permitting Considerations ............................................................................................................................ 14 2.7 Financial and Economic Aspects to Sediment Management for Reservoirs ............................. 16 3 Reservoir Sedimentation Management by Means of Dredging .................................. 17 3.1 Design Parameters for Reservoir Dredging Operations .................................................................... 17 3.2 Available Resources for Planning and Design ....................................................................................... 18 3.3 Dredging Technologies Overview .............................................................................................................. 19 3.4 Selection of Target Areas of Reservoir for Dredging ......................................................................... 20 3.5 Mechanical Dredging Operations for Removal of Reservoir Sediment ...................................... 21 3.6 Hydraulic Dredging Operations for Removal of Reservoir Sediment .......................................... 24 3.7 Water Management for Hydraulic Dredging Operations ................................................................. 32 4 Options for Placement or Disposal of Removed Sediment ......................................... 34 4.1 Upland Confined Placement ........................................................................................................................ 35 4.2 Downstream Placement ................................................................................................................................. 37 4.3 Beneficial Use ..................................................................................................................................................... 39 4.4 Management and Disposal of Chemically Impacted Sediment ..................................................... 40 5 Costs of Reservoir Dredging ................................................................................................ 42 5.1 General Cost Drivers ....................................................................................................................................... 42 Reservoir Dredging: A Practical Overview 2 April 2021 5.2 Cost Management (in different stages of the process) ..................................................................... 43 5.3 Example Cost Ranges from Recent Reservoir Dredging Projects in the United States......... 44 6 New Technologies for Reservoir Dredging ...................................................................... 45 6.1 Anticipated Key Areas for Innovation Focus .......................................................................................... 45 6.2 Innovative Approach to Dredging Controls ........................................................................................... 47 6.3 Innovative Approach to Deep Reservoir Dredging and Material Pumping ............................... 48 6.4 Innovative Approaches to Sediment Removal and Transport from Lakebed ........................... 50 6.5 Innovative Approaches for Dredge Portability and Footprint Reduction .................................. 54 6.6 Innovative Approaches for Sediment Capture (before entering reservoir) ............................... 55 6.7 Opportunities for Development of New Technologies ..................................................................... 58 7 Conclusions and Final Take-Away Message..................................................................... 60 8 References ................................................................................................................................. 61 TABLES Table 1 ……………………………………………………………………………………………………………………24 Reservoir Dredging: A Practical Overview 3 April 2021 FIGURES Figure 1 Longitudinal Pattern of Sediment Composition Typically Found in a Reservoir 5 Figure 2 Changes to United States Capacity Over Time Due to Dam Construction and Reservoir Sedimentation 8 Figure 3 Reservoir Storage Capacity Over Time Due to Dam Construction, Reservoir Sedimentation, and Population Increase 9 Figure 4 Classification of Methods to Manage Reservoir Sedimentation 12 Figure 5 Reservoir Water Allocation Definitions 21 Figure 6 Mechanical Dredge Consisting of a Crane Using a Clamshell Bucket 22 Figure 7 Mechanical Dredge Consisting of a Hydraulic Excavator Using a Hydraulically Activated Bucket 23 Figure 8 Conventional Cutterhead Suction Dredge 26 Figure 9 Swinging Ladder Cutterhead Suction Dredge 26 Figure 10 System Components of a Swinging Ladder Cutterhead Suction Dredge Depositing Slurry in a Confined Disposal Facility 27 Figure 11 22-Inch Electric Cutter Suction Dredge LP at John Redmond Reservoir in Kansas 29 Figure 12 Booster Pump Station at Lake Decatur, Illinois 30 Figure 13 Hydraulic Dredging with Cable-Supported Submersible Pump 31 Figure 14 Example of Dredge with Ladder-Supported Submersible Pump 31 Figure 15 Dredge with Ladder-Supported Submersible Pump and Other Components 32 Figure 16 Example of Confined Upland Placement Area for Sediments 36 Figure 17 Example Confined Upland Placement Area for Sediments 37 Figure 18 Illustration of a Hydraulic Dredge Using Multibeam Sonar Imaging 47 Figure 19 Multibeam Sonar Imaging Underwater Infrastructure to Improve Dredging Accuracy and Production. 48 Figure 20 Ambiesta Dam Dredging Concept 49 Figure 21 Ambiesta Reservoir Dredging Design 50 Figure 22 Differential Head Operating Principal of a Siphon Dredge 51 Figure 23 Modified Hydrosuction Dredge in Operation 52 Figure 24 Modified Hydrosuction Water Jetting Array 52 Figure 25 Illustration of Sediment Being Transported in a Density Current Generated by a WID 54 Figure 26 Example of Self-Launching “Portable” Dredge Equipment 55 Figure 27 BI-T Collector Installed in Fountain Creek, Pueblo, Colorado, and Shore Sediment Re- Handling Plant 57 Figure 28 Small-Scale BI-T Deployed in a Proof-of-Concept Demonstration Upstream of the Strontia Springs Reservoir 58 Reservoir Dredging: A Practical Overview 4 April 2021 1 Introduction This technical report provides an overview of the dredging process as applied to reservoirs: the unique technologies and respective capabilities, challenges, and engineering and environmental considerations that apply. As a starting point for the reader, some basic definitions are in order. First of all, dredging is defined as the subaqueous or underwater excavation of soils and rock. The dredging process can be separated into four phases: excavation, vertical transport, horizontal transport, and placement or use of the material dredged. Dredging can be done for many different reasons or purposes. This report is specifically focused on the possible dredging of water storage reservoirs where the storage capacity provides beneficial uses (e.g., water supply for irrigation,